/Engine/Source/Runtime/TimeManagement/Public/TimeSynchronizationSource.h
Calculates the distance between two frames. This method accounts for rollover (when used), and assumes the frames will always be relatively close together. This is also a convenient method to use to check whether or not a rollover has happened within a range of frames.
static int32 FindDistanceBetweenFramesWithRolloverModulus ( const [FFrameTime](API\Runtime\Core\Misc\FFrameTime) & StartFrameTime, const [FFrameTime](API\Runtime\Core\Misc\FFrameTime) & EndFrameTime, const [TOptional](API\Runtime\Core\IO\TOptional)< [FFrameTime](API\Runtime\Core\Misc\FFrameTime) > & RolloverModulus, bool & bDidRollover )